Usually, a diesel vehicle emits more exhaust gas in comparison to a gasoline vehicle. Also, a diesel vehicle is noisy and tends to vibrate more. Accordingly, the diesel engine is equipped with a Diesel Particulate Filter (DPF) to reduce the exhaust gas, and introduces multi-pilot injection to reduce noise and vibration. In addition, various means for improving the combustion process are being introduced in the diesel vehicle.
Specifically, to reduce combustion noise of the diesel vehicle, hardware aspects of the vehicle such as hardness of the vehicle, shielding, and sound-absorbing materials have been improved in recent years. Also, in terms of software, fuel injection factors such as an injection pressure, injection timing, a fuel amount, and the like, are determined depending on engine rpm and loads, and these fuel injection factors are corrected depending on environmental variables (for example, ambient temperature, atmospheric pressure, and coolant temperature). Then, the fuel injection is carried out according to the fuel injection factors. Additionally, to reduce combustion noise, a combustion pressure rise rate is decreased by increasing the number of pilot fuel injections. The pilot injection involves creating a combustion condition (increasing the temperature of a combustion chamber to mix fuel and air well) before a main fuel injection, and may reduce ignition delay and decrease the combustion fuel pressure rise that is caused by the main fuel injection.
Also, in case of the diesel engine, coking may occur. That is, due to aging of an injection quantity adaptation injector, a fuel injecting hole becomes clogged by exhaust gas. Accordingly, in response to the same commands of an ECU, the quantity of injected fuel is actually smaller than before and thus an abnormal combustion noise (engine knocking noise) occurs. Consequently, in the case where a pilot fuel quantity is small, a technique for increasing the pilot fuel quantity is necessary.
The foregoing is intended merely to aid in the understanding of the background of the present invention, and is not intended to mean that the present invention falls within the purview of the related art that is already known to those skilled in the art.
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